1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a method of producing an electrophotographic photosensitive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
An electrophotographic photosensitive member using an organic photoconductive substance (organic electrophotographic photosensitive member) has the following advantages: the organic electrophotographic photosensitive member can be easily produced as compared with an electrophotographic photosensitive member using an inorganic photoconductive substance (inorganic electrophotographic photosensitive member), and has a higher degree of freedom in functional design than the inorganic electrophotographic photosensitive member because a material for the organic electrophotographic photosensitive member can be selected from a wide variety of materials. With the advent of rapid widespread of laser beam printers in recent years, such organic electrophotographic photosensitive member has come to be widely used in the market.
A general electrophotographic photosensitive member has a support and a photosensitive layer formed on the support. In addition, a laminated photosensitive layer obtained by superimposing in this order from the support side a charge-generating layer containing a charge-generating substance and a hole-transporting layer containing a hole-transporting substance has been often used as the photosensitive layer.
In addition, an intermediate layer is often provided between the support and the photosensitive layer for the purpose of, for example, improving adhesiveness between the support and the photosensitive layer, protecting the photosensitive layer from electrical breakdown, or inhibiting holes from being injected from the support into the photosensitive layer.
Although such an intermediate layer has the above-mentioned merit, the intermediate layer involves the following demerit: charge is apt to accumulate in the intermediate layer. When image formation is repeatedly performed for a long time period, the accumulation of charge in the intermediate layer has increased a potential variation to cause problems in an output image in some cases.
Japanese Patent Application Laid-Open No. 2005-134924, Japanese Patent Application Laid-Open No. 2005-221923, and Japanese Patent Application Laid-Open No. 2007-148357 each disclose a technique for alleviating a potential variation or suppressing interference fringes by incorporating surface-treated titanium oxide particles each having a small particle diameter into an intermediate layer. However, there is still room for improvement in terms of the potential variation when image formation is repeatedly performed for a long time period.
In addition, Japanese Patent Application Laid-Open No. S58-93062, Japanese Patent Application Laid-Open No. S59-84257, Japanese Patent Application Laid-Open No. H09-90661, and Japanese Patent Application Laid-Open No. 2000-66432 each disclose a technique for reducing a potential variation such as an increase in residual potential or a reduction in initial potential when image formation is repeatedly performed by using an electrophotographic photosensitive member having an intermediate layer. In the existing circumstances, however, demerits such as deterioration in initial sensitivity or deterioration in chargeability are involved, so the problems have not been sufficiently solved yet.